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Thermochemistry
 
 
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In thermodynamics
Thermodynamics

In physics, thermodynamics is the study of the conversion of heat energy into different forms of energy ; different energy conversions into heat energy; and its relation to macroscopic variables such as temperature, pressure, and volume....
 and physical chemistry
Physical chemistry

Physical chemistry is the application of physics to macroscopic, microscopic, atomic, subatomic, and particulate phenomena in chemical systems within the field of chemistry traditionally using the principles, practices and concepts of thermodynamics, quantum chemistry, statistical mechanics and kinetics....
, thermochemistry is the study of the energy
Energy

In physics, energy is a scalar physical quantity that describes the amount of Work_ that can be performed by a force. Energy is an attribute of objects and systems that is subject to a conservation law....
 evolved or absorbed in chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
s and any physical transformations, such as melting
Melting

Melting is a process that results in the phase change of a substance from a solid to a liquid. The internal energy of a solid substance is increased to a specific temperature at which it changes to the liquid phase....
 and boiling
Boiling

Boiling, a type of phase transition, is the rapid vaporization of a liquid, which typically occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding environmental pressure....
. Thermochemistry, generally, is concerned with the energy exchange accompanying transformations, such as mixing, phase transition
Phase transition

In thermodynamics, a phase transition is the transformation of a thermodynamic system from one phase to another.At phase-transition point, physical properties may undergo abrupt change- for instance, volume of the two phases may be vastly different....
s, chemical reactions, and including calculations of such quantities as the heat capacity, heat of combustion
Heat of combustion

The heat of combustion is the energy released as heat when one mol of a compound undergoes complete combustion with oxygen. The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon dioxide, water and heat....
, heat of formation, enthalpy
Enthalpy

In thermodynamics and chemistry, the enthalpy is a quotient or description of thermodynamic potential of a system, which can be used to calculate the heat transfer during a quasistatic process taking place in a closed system thermodynamic system under constant pressure....
, and free energy.
mochemistry rests on two generalizations:

  1. Lavoisier and Laplace’s law (1782): the heat exchange accompanying a transformation is equal and opposite to the heat exchange accompanying the reverse transformation.
  2. Hess's law
    Hess's law

    Hess's law is a relationship from physical chemistry named for Germain Henri Hess, a Swiss-born Russian chemist and Physician. The law is based on the principle of conservation of energy and the path independence of energy changes....
     (1840): the heat exchange accompanying a transformation is the same whether the process occurs in one or several steps


Both of these statements preceded the first law of thermodynamics
First law of thermodynamics

In thermodynamics, the first law of thermodynamics is an expression of the more universal physical law of the conservation of energy. Succinctly, the first law of thermodynamics states:...
 (1850) and helped in its formulation.

Lavoisier, Laplace and Hess also investigated specific heat and latent heat
Latent heat

In thermochemistry, latent heat is the amount of energy in the form of heat released or absorbed by a chemical substance during a change of state of matter , or a phase transition....
, although it was Joseph Black
Joseph Black

Joseph Black was a Scottish physician, physicist, and chemist, known for his discoveries of latent heat, specific heat, and carbon dioxide. He was a founder of thermochemistry who developed many pre-thermodynamics concepts, such as heat capacity, and was the mentor for James Watt....
 who made the most important contributions to the development of latent energy changes.
measurement of heat changes is performed using calorimetry
Calorimetry

Calorimetry is the science of measuring the heat of chemical...
, usually an enclosed chamber within which the change to be examined occurs.






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Encyclopedia


In thermodynamics
Thermodynamics

In physics, thermodynamics is the study of the conversion of heat energy into different forms of energy ; different energy conversions into heat energy; and its relation to macroscopic variables such as temperature, pressure, and volume....
 and physical chemistry
Physical chemistry

Physical chemistry is the application of physics to macroscopic, microscopic, atomic, subatomic, and particulate phenomena in chemical systems within the field of chemistry traditionally using the principles, practices and concepts of thermodynamics, quantum chemistry, statistical mechanics and kinetics....
, thermochemistry is the study of the energy
Energy

In physics, energy is a scalar physical quantity that describes the amount of Work_ that can be performed by a force. Energy is an attribute of objects and systems that is subject to a conservation law....
 evolved or absorbed in chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
s and any physical transformations, such as melting
Melting

Melting is a process that results in the phase change of a substance from a solid to a liquid. The internal energy of a solid substance is increased to a specific temperature at which it changes to the liquid phase....
 and boiling
Boiling

Boiling, a type of phase transition, is the rapid vaporization of a liquid, which typically occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding environmental pressure....
. Thermochemistry, generally, is concerned with the energy exchange accompanying transformations, such as mixing, phase transition
Phase transition

In thermodynamics, a phase transition is the transformation of a thermodynamic system from one phase to another.At phase-transition point, physical properties may undergo abrupt change- for instance, volume of the two phases may be vastly different....
s, chemical reactions, and including calculations of such quantities as the heat capacity, heat of combustion
Heat of combustion

The heat of combustion is the energy released as heat when one mol of a compound undergoes complete combustion with oxygen. The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon dioxide, water and heat....
, heat of formation, enthalpy
Enthalpy

In thermodynamics and chemistry, the enthalpy is a quotient or description of thermodynamic potential of a system, which can be used to calculate the heat transfer during a quasistatic process taking place in a closed system thermodynamic system under constant pressure....
, and free energy.

History

Thermochemistry rests on two generalizations:

  1. Lavoisier and Laplace’s law (1782): the heat exchange accompanying a transformation is equal and opposite to the heat exchange accompanying the reverse transformation.
  2. Hess's law
    Hess's law

    Hess's law is a relationship from physical chemistry named for Germain Henri Hess, a Swiss-born Russian chemist and Physician. The law is based on the principle of conservation of energy and the path independence of energy changes....
     (1840): the heat exchange accompanying a transformation is the same whether the process occurs in one or several steps


Both of these statements preceded the first law of thermodynamics
First law of thermodynamics

In thermodynamics, the first law of thermodynamics is an expression of the more universal physical law of the conservation of energy. Succinctly, the first law of thermodynamics states:...
 (1850) and helped in its formulation.

Lavoisier, Laplace and Hess also investigated specific heat and latent heat
Latent heat

In thermochemistry, latent heat is the amount of energy in the form of heat released or absorbed by a chemical substance during a change of state of matter , or a phase transition....
, although it was Joseph Black
Joseph Black

Joseph Black was a Scottish physician, physicist, and chemist, known for his discoveries of latent heat, specific heat, and carbon dioxide. He was a founder of thermochemistry who developed many pre-thermodynamics concepts, such as heat capacity, and was the mentor for James Watt....
 who made the most important contributions to the development of latent energy changes.

Calorimetry

The measurement of heat changes is performed using calorimetry
Calorimetry

Calorimetry is the science of measuring the heat of chemical...
, usually an enclosed chamber within which the change to be examined occurs. The temperature of the chamber is monitored either using a thermometer
Thermometer

The thermometer is a device that measures temperature or temperature gradient using a variety of different principles; it comes from the Greek language roots thermo, heat, and meter, to measure....
 or thermocouple
Thermocouple

A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference. Thermocouples are a widely used type of list of temperature sensors and can also be used to convert heat into electric power....
, and the temperature plotted against time to give a graph from which fundamental quantities can be calculated. Modern calorimeters are frequently supplied with automatic devices to provide a fast read-out of information, one example being the DSC or differential scanning calorimeter.

See also

  • Differential scanning calorimetry
    Differential scanning calorimetry

    Differential scanning calorimetry or DSC is a thermal analysis technique in which the difference in the amount of heat required to increase the temperature of a sample and reference are measured as a function of temperature....
  • Important publications in thermochemistry
  • Isodesmic reaction
    Isodesmic reaction

    An isodesmic reaction is a chemical reaction in which the type of chemical bonds broken in the reactant are the same as the type of bonds formed in the reaction product....
  • Principle of maximum work
    Principle of maximum work

    In the history of science, the principle of maximum work was a postulate concerning the relationship between chemical reactions, heat evolution, and the potential thermodynamic work produced there from....
  • Reaction Calorimeter
    Reaction Calorimeter

    A reaction calorimeter is an Measuring instrument that enables the energy being Exothermic or Endothermic by a Chemical reaction to be measured. The majority of events taking place within a reactor release or absorb energy, so if that can be measured it allows a view of what is taking place to be gained....
  • Thomsen-Berthelot principle
    Thomsen-Berthelot principle

    In thermochemistry, the Thomsen-Berthelot principle is an hypothesis in the history of chemistry which argued that all chemical process are accompanied by the production of heat and that processes which occur will be ones in which the most heat is produced....
  • Julius Thomsen
  • Thermodynamic databases for pure substances
    Thermodynamic databases for pure substances

    Thermodynamics databases contain information about List of thermodynamic properties for substances, the most important being enthalpy, entropy, and Gibbs free energy....
  • Calorimetry
    Calorimetry

    Calorimetry is the science of measuring the heat of chemical...


External links

  • - Britannica (1911)
  • - an overview